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Reading a certificate of analysis line by line
Sep
A certificate of analysis answers four questions in a fixed order: which batch was tested, whether it is the right molecule, how much of the detected material is that molecule, and who stands behind the result.
Read it as evidence about one batch, not a description of a product. Every line either ties back to the vial in your hand or it does not.
This guide walks a peptide certificate of analysis from the header to the signature and names the question each section answers. It pairs with our explainer on what a purity number on a certificate actually measures, which goes deeper into the chromatography behind the headline figure.
Laboratories order the sections differently, but the content is the same.
How a peptide certificate of analysis is laid out
Each block on the page answers one question, and each answer rests on a named method. Where a block is missing, its question stays open.
| Section | Question it answers | Typical method |
|---|---|---|
| Header | Which material, which batch, tested when and by whom | The laboratory’s sample log and report ID |
| Identity | Is the main component the expected molecule | LC-MS, observed mass against calculated mass |
| Purity | What share of the UV signal is the target peptide | RP-HPLC, area percent at a stated wavelength |
| Content fields | How much of the powder is peptide, water or counterion | Mass balance, Karl Fischer titration, ion chromatography |
| Endotoxin | Is bacterial endotoxin present above a stated limit | Bacterial endotoxins test, USP <85> |
| Signature | Who is responsible for the result | Signed report, accreditation certificate and scope |
The header carries the product and its sequence, the batch or lot number, the test date, the laboratory’s name and a report ID. The batch number anchors everything below it.
- Batch or lot number. It should match the number printed on the vial, character for character.
- Test date. It should fall after the batch was made. A date years earlier means the report belongs to other material.
- Laboratory name. A named laboratory can be contacted and checked. An unnamed one cannot.
- Report or sample ID. The laboratory’s own reference, which lets it confirm that it issued the report.
Identity: expected mass against observed mass
LC-MS separates the sample, then measures the mass of its ions. The certificate should list the mass calculated from the sequence and the mass the instrument observed. A match within the stated tolerance shows that the main component has the mass the sequence predicts.
ICH Q2(R2) expects an identification test to rest on unique aspects of molecular structure, and it recommends combining two or more procedures when one does not discriminate well enough. Mass alone has known blind spots.
Leucine and isoleucine are isomers with the same mass, and a sequence with two residues swapped keeps the same composition. The USP methods summarized by McCarthy and colleagues list amino acid analysis to distinguish isoleucine from leucine, a chirality test to confirm D amino acids, and LC-MS/MS or NMR to confirm sequence and structure.
A mass match also says nothing about how much of the sample is the target molecule. That is the purity section’s job.
Purity: the number and the trace behind it
Purity on a peptide certificate is usually RP-HPLC area percent: the main peak’s area divided by the total area of all peaks detected at one UV wavelength. The line should name the method, the column and the wavelength, and a chromatogram should be attached. Without the trace, the number cannot be checked.
- Method and column. RP-HPLC on a C18 column is the common setup for peptides. A line that says only HPLC leaves out the conditions that shape the result.
- Wavelength. The figure holds at the wavelength stated. An impurity that absorbs weakly there adds little area, whatever its weight.
- Chromatogram. The trace shows the main peak, the small peaks around it and the baseline. ICH Q2(R2) treats representative chromatograms as the evidence that a method separates what it claims to separate.
Area percent is a share of UV signal, not of powder weight. Water and counterions need other methods, covered next.
Optional fields and what their absence means
Some certificates go further and describe the rest of the powder, because a lyophilized peptide is not all peptide. Peptides cleaved and purified with trifluoroacetic acid are obtained as trifluoroacetate salts, and the same review notes that TFA can interfere with physicochemical characterization and with experiments involving mammalian cells.
Net peptide content
The share of the powder’s weight that is the peptide itself. In the USP reference standard work cited above, it is assigned by mass balance: impurities, counterion, water, residual solvents and inorganic residue are measured and subtracted from 100 percent.
Water content
Residual moisture in the lyophilized cake. The same USP work measured it by Karl Fischer titration under USP general chapter <921>.
Counterion content
The acetate, trifluoroacetate or chloride held by charged residues. Mrozik and colleagues compared ion chromatography with two electrophoretic methods for measuring it and found ion chromatography gave the best results.
Endotoxin is reported when the laboratory ran the bacterial endotoxins test of USP <85>, which FDA guidance discusses along with its gel clot, photometric and kinetic test methods. Appearance is a plain description, such as a white lyophilized powder.
An absent field means the test was not reported, not that the result was good. A certificate with no water or counterion line gives no basis for converting powder weight into peptide weight.
The signature and the laboratory’s accreditation
The signature names the person at the laboratory who reviewed and released the result. A signed report on the laboratory’s letterhead ties the numbers to an organization that can be asked about them. A seller’s retyped summary does not.
Accreditation to ISO/IEC 17025 is the usual outside check. The standard sets out requirements for the competence, impartiality and consistent operation of laboratories.
Accreditation covers listed tests, not a laboratory as a whole. A2LA defines the scope of accreditation as the list of specific tests for which a laboratory was found competent, and states that capabilities not listed on the scope are not covered by its accreditation.
A laboratory accredited for one assay can run HPLC purity outside its scope. Ask for the scope document and look for the method named on the report.
Red flags, and matching the certificate to the vial
A certificate that fails any of these checks cannot be tied to the vial in hand with confidence.
- No batch or lot number on the certificate
- No method, column or wavelength named for purity
- The same certificate shown for more than one batch
- No testing laboratory named, or only the seller’s name
- A purity figure with no chromatogram attached
- A test date long before the batch was made
- An observed mass with no expected mass beside it
Federal drug manufacturing rules show how far a supplier’s paperwork is trusted. Under 21 CFR 211.84, a manufacturer may accept a report of analysis from the supplier of a component only if it runs at least one specific identity test itself and validates the supplier’s results at appropriate intervals. The logic holds for any certificate: it is a claim, checked against something independent.
For the reader, the first independent check is the label. Imperial Biolab prints a batch number on every vial, and the QR code on the label opens the certificate for that exact batch, with the testing laboratory, test date, method, results and the laboratory’s own signed report. Certificates stay online after a batch sells out, and the full set is in the certificate library.
The second check is the box itself, covered in cold chain in transit and the first hour after a box arrives. If a label and a certificate do not match, contact the team with the batch number.
- The header ties every result to one batch, one date and one named laboratory
- An LC-MS mass match confirms mass, not sequence order or isomers
- RP-HPLC purity is a share of UV signal and needs its chromatogram
- Water, counterion and net peptide content describe the rest of the powder
- ISO/IEC 17025 accreditation counts only for methods on the laboratory’s scope
- The batch number on the vial must match the certificate exactly
Frequently asked questions
At minimum: the product, a batch or lot number, a test date, the testing laboratory’s name, an identity result by LC-MS with expected and observed mass, and a purity result by RP-HPLC with the method, column, wavelength and an attached chromatogram. Water, counterion, net peptide content and endotoxin are optional additions.
No. It shows the main component has the expected mass. Isomeric residues such as leucine and isoleucine share a mass, and a sequence with residues swapped has the same composition. Confirming sequence and structure needs further methods, such as LC-MS/MS sequencing, amino acid analysis or NMR.
Many certificates report only identity and purity. Net peptide content needs a mass balance that measures water, counterion, impurities and residue separately and subtracts them. Its absence does not mean the value is low or high. It means the report gives no basis for converting the weight of powder into the weight of peptide.
It means an accreditation body assessed the laboratory’s competence, impartiality and consistent operation for a defined list of tests. That list is the scope. A result is covered only when its method appears on the scope, so check the scope document for the HPLC and LC-MS methods named on the report.
It should not. A certificate reports results for the sample the laboratory tested, identified by one batch number and one test date. A report reused across batches, or dated long before the batch existed, describes other material. Match the batch number on the vial to the certificate character for character.
- ICH Q2(R2) Validation of analytical procedures. ICH, November 2023. View source
- McCarthy D, Han Y, Carrick K, et al., 2023. Reference Standards to Support Quality of Synthetic Peptide Therapeutics. Pharmaceutical Research, 40(6), 1317 to 1328. DOI
- Sikora K, Jaśkiewicz M, Neubauer D, et al., 2020. The Role of Counter-Ions in Peptides: An Overview. Pharmaceuticals, 13(12), 442. DOI
- Mrozik W, Markowska A, Guzik L, et al., 2012. Determination of counter-ions in synthetic peptides by ion chromatography, capillary isotachophoresis and capillary electrophoresis. Journal of Peptide Science, 18(3), 192 to 198. DOI
- Pyrogen and Endotoxins Testing: Questions and Answers (Edition 2). FDA, March 2026. View source
- ISO/IEC 17025:2017 General requirements for the competence of testing and calibration laboratories. ISO, 2017. View source
- Frequently Asked Questions: What is the scope of accreditation. A2LA. View source
- 21 CFR 211.84 Testing and approval or rejection of components, drug product containers, and closures. eCFR. View source
This article is general educational information about laboratory analysis and material handling. It is not medical, legal or regulatory advice, and nothing in it describes or recommends the use of any compound in people or animals. Materials supplied by Imperial Biolab are for research use only: not for human or veterinary use, not for diagnostic use, and not for use as a food, drug, dietary supplement or cosmetic. Sale is restricted to adults aged 21 or over. See the research use disclaimer for details.
